Decay, or caries of the teeth, is an exceedingly common affection. It is generally produced by decomposition of portions of food left between the teeth, which undergo decomposition, developing lactic acid, which has the power to dissolve the enamel. When the teeth are only slightly diseased, and even when quite badly affected with caries, much good may be done by having the teeth properly filled by a competent dentist. When the teeth become so bad that filling is out of the question or useless, it may become necessary to have them drawn. The teeth should be saved whenever it is possible to do so. It is rarely necessary to use an anaesthetic in drawing teeth, though nitrous oxide is much used for this purpose. A recently proposed substitute for anaesthetics in these cases is rapid breathing. In employing this method, the patient should breathe about one hundred times a minute, keeping up the respiration during the whole operation.